Variable capacitive apparatus

ABSTRACT

A variable capacitance apparatus particularly adapted for use with a manually-operated keyboard and having two parallel, conductive plates with a dielectric therebetween. Depression of a key moves one conductive plate farther from the other conductive plate so as to reduce the capacitive coupling between the conductive plates, in order to determine whether the key has been depressed.

United States Patent Leno [ 1 June 20, 1972 [54] VARIABLE CAPACITIVEAPPARATUS [21] App1.No.: 99,186

[52] US. Cl ..317/249 R, ZOO/DIG. 1, 317/246, 317/250 [51] Int. Cl...II0lg 5/10 [58] Field of Search ..317/249 R, 246, 245, 250; 200/DIG. 1

[56] References Cited UNITED STATES PATENTS 2,179,068 11/1939 Sprague..317/249 R 2,744,222 4/1956 Toomin ..317/249 R 3,183,912 5/1965Mogilner... ...317/249 R X 3,230,431 l/l966 Deniston... ..317/249 R3,293,640 12/1966 Chalfin ..317/246 X 3,488,565 1/1970 Teltscher......317/249 R X 3,551,860 12/1970 Smimov ..317/249 R X FOREIGN PATENTS ORAPPLICATIONS 351,686 9/1920 Germany ..317/245 Primary Examiner-E. A.Goldberg Attorney-J. L. Landis and R. P. Miller [5 7] ABSTRACT Avariable capacitance apparatus particularly adapted for use with amanually-operated keyboard and having two parallel, conductive plateswith a dielectric therebetween. Depression of a key moves one conductiveplate farther from the other conductive plate so as to reduce thecapacitive coupling between the conductive plates, in order to determinewhether the key has been depressed.

18 Claims, 5 Drawing Figures 2,432,089 12/1947 Carter ..3l7/249R2,438,477 3/1948 Dodds.. .....317/249RX 2,543,570 2/1951 Eder..3l7/249RX 2,589,351 3/1952 Ehrlich ..317/249R I 5o-l,.

PLATES DIELECTRIC MAGNET WIS PATENTEMunzo Ian FIG. I

ATTORNEY VARIABLE CAPACITIVE APPARATUS FIELD OF THE INVENTION Thisinvention relates to electrical switching apparatus and method and moreparticularly to a switching apparatus and method in which the switchingaction involves the change of capacitive coupling between two conductiveplates.

BACKGROUND OF THE INVENTION It is well known in the prior art ofkeyboards that the depression of a key can be used to mechanically closean electrical contact switch in order to indicate to some form ofutilization circuitry that the key has been depressed. However, inconnection with modern electronic circuitry, conventional electricalcontacts have serious limitations due to lint, phenolic vapors,moisture, corrosion and other problems which tend to reduce thereliability of contact closure, especially under low voltage conditionsnormally associated with transistor circuitry.

Therefore, it is an object of the present invention to provide a morereliable switching device.

It is another object of the present invention to provide a switch whichis relatively insensitive to ordinary atmospheric conditions.

It is a further object of the present invention to provide anelectronically detectable indication of a manual input.

SUMMARY OF THE INVENTION In accordance with present invention, avariable capacitor comprises a first planar conductive surface and asecond conductive surface separated therefrom by dielectric materialwherein thedistance'between the first and second conductive surfaces isvaried in order to vary the capacitive coupling between the conductors.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of thepresent invention maybe had by reference to the following detaileddescription when considered, in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a cross-sectional view showing a manually-movable,magnetically-biased, key-operated capacitor plate that is held intoengagement with a dielectric-covered companion electrode plate;

FIG. 2 is similar to FIG. 1, but showing the key partially depressed;

FIG. 3 is crosssectional view of an alternate embodiment in which themovable capacitor plate is pivoted on a flexure 'oint; J FIG. 4 showsanother alternative embodiment having a hinged pivot in which thecapacitor plates are magnetically biased away from each other and showsa circuit for determining capacitive coupling; and

FIG. 5 shows an embodiment similar to that shown in FIG. 4, but with apush-push mechanism comparable to that used in a retractable ball-pointpen.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the accompanyingdrawings and more particularly to FIGS. 1 and 2, a plastic housingcontains a pair of steel, magnetic shielding plates 12 on the interiorsurfaces of opposite sides of the plastic housing 10. Two permanentmagnets 14 and 16 are placed in the housing next to the shielding plates12. A pair of bronze, fixed electrode plates 18 and 20 are bonded eachto one face of the magnets 14 and 16, respectively, and have connectortabs projecting out of the bottom of the plastic housing 10. Adielectric material 22 is used to coat those surfaces of the fixedplates 18 and 20 which face toward the center of the plastic housing 10.

A pair of bent, ferromagnetic, electrode swing plates 24 and 26 areplaced so that they can pivot on the bottom of the plastic housing 10and are magnetically attracted by the permanent magnets 14 and 16,respectively, to positions wherein they press against the dielectricsurfaces 22. A common pin 30 extends through the bottom of the plastichousing 10 between the two swing plates 24 and 26. A flexible electricalconnection 32 is made between the common pin 30 and each of the swingplates.

In a normal or unenergized condition as shown in FIG. 1, the capacitancebetween the common pin 30 and either of the fixed electrode plates 18 or20 is at a maximum. If the capacitance were suitably sampled at thistime, it would indicate that the plates 24 and 26 were in theirunenergized position; because, a maximum of electrical energy would becoupled through the capacitors formed by the plates 24 and 18 and by theplates 26 and 20.

A keytop 40, FIG. 1, is connected by a push rod 42 to the interior ofthe plastic housing 10. A shoulder 44 on the push rod 42 is inengagement with a trip spring 46 which is also in engagement with thebent-over portion of the swing plate 26. Similarly, a shoulder 48 on thepush rod 42 is connected by a spring 50 to the bent-over portion of theswing plate 24.

As the keytop is manually depressed, the trip springs 46 and 50 arecompressed and exert increasing amounts of force upon the bent-overportions of their associated swing plates 24 and 26. The trip spring 46is so constructed that, upon depression of the keytop 40 to the positionshown in FIG. 2, the spring 46 finally builds up a sufficient force toovercome the magnetic attraction of the permanent magnet 16, therebycausing the swing plate 26 to separate from its associated dielectricsurface 22 as shown in FIG. 2. The trip spring 50 is so constructed thatonly upon still further depression of the keytop 40 to the positionindicated by the dotted lines 51 in FIG. 2 following the separation ofthe swing plates 26, is sufficient force exerted by the trip spring 50on the bent-over por tion of the swing plate 24 to cause the swing plate24 to separate from its associated fixed plate 18.

Therefore, as the keytop 40 is initially depressed, nothing happens atfirst. However, continued depression of the keytop 40 to the positionshown in FIG. 2 causes the swing plate 26 to separate from itsassociated fixed plate 20. Further, continued depression then causes theswing plate 24 also to separate from its associated fixed plate 18.

In a typewriter keyboards, it is sometimes desired to provide a facilityfor repeating a character in response to a further depression of the keyagainst an increased spring force. It will be appreciated that theembodiment shown in FIG. I and 2 is capable of providing one output upona normal depression of the keytop 40 and of providing a second output tocause repetition of a character upon further depression of the same key.

As an alternative embodiment of the present invention, reference may behad to FIG. 3 wherein the permanent magnet 16 is connected to fixedelectrode 52, and the surface of the magnet 16 itself is one plate ofthe capacitor. A ferromagnetic swing plate 54 is mounted to an electrode56 by a tlexure joint 58. A keytop 40 is constructed so as to fit aroundthe outside of the plastic housing 10. A trip spring 46 is connectedbetween the keytop 40 and the swing plate 54. In the normal, unactuatedposition of the switch of FIG. 3, the magnet 16 attracts and holds theswing plate 54 firmly against the dielectric material 22 to assuremaximum capacitive coupling between the electrodes 52 and 56.

Upon depression of the keytop 40, nothing happens initially except thecompression of the spring 46. Upon continued depression of the keytop40, sufficient force is finally applied by the spring 46 to the swingarm 54 to overcome the attraction of the permanent magnet 16. The swingplate 54 then separates from the magnet 16 and dielectric 22 and rotatesclockwise (as shown in FIG. 3) bending the flexure joint 58. Thus, thecapacitive coupling between the electrodes 52 and 56 is sharply reduced.Suitable electronic circuitry can then be electrodes.

Referring now to FIG. 4, still another alternative embodiment of thepresent invention is illustrated. A permanent magnet 16 is firmlymounted within a housing on a conductive framework connected to anelectrode 62. A ferromagnetic, conductive swing plate 64 is rotatablymounted on a pivot 66 and is normally attracted by the magnet 16. Aflexible electrical connection 68 assures electrical continuity betweenthe electrode 62 and the swing plate 64.

As the keytop 40 is depressed, the spring 46 is compressed untilsufficient force is exerted by the spring 46 on an arm of the plate 64to overcome the magnetic attraction of the permanent magnet 16. Thispermits the swing plate 64 to separate from the magnet 16 and rotateunder the urging of the spring 46 clockwise about-the pivot 66 until theswing plate 64 is parallel to and abutting a dielectric material 22 onthe surface of a fixed electrode 70.

In the embodiment shown in FIG. 4, the capacitive coupling between theelectrodes 62 and 70 is minimum in the deenergized condition of theswitch. However, when the keytop 40 is fully depressed, the swing plate64 is in closer proximity to the fixed electrode 70, resulting inincreased capacitive coupling between the electrodes 62 and 70.

Many variations are possible on all three of the embodiments shown. FIG.is a variation which is illustrated -with respect to the structure ofFIG. 4 but which might readily be applied to the embodiments shown inFIGS. 1, 2 and 3.

Referring now to FIG. 5, a push-to-latch, push-to-release cam 80 ismounted on the plastic housing 10. The keytop 40 is connected to the camfollower 82 and is thus held in the depressed condition every secondtime that it is depressed. Push-push mechanisms such as the cam 80 andfollower 82 are well known in the prior art and will not be describedfurther herein.

One typical capacitance sampling circuit 90 is shown in connection withthe structure of FIG. 4. The circuit 90 could be used equally well withthe structures of FIGS. 1, 2 and 3. Other types of capacitance samplingcircuits will be readily apparent to one of ordinary skill in the art.

In FIG. 4, an AC generator 92 delivers a constant amplitude AC signal tothe electrode 70. The input of a rectifying detector 94 is connected tothe electrode 62, and the detector 94 delivers an output that is a DCvoltage having a magnitude that is representative of the amplitude ofthe AC voltage coupled from the electrode 70 to the electrode 62. Anamplifier 96 delivers an amplified DC signal to a Schmitt Trigger 98 orother voltage thresholdsensor which produces an output signal only whenits signal input exceeds a predetermined magnitude. The voltage levelscan then be predetermined or adjusted at such magnitudes that theSchmitt trigger will produce an output voltage only when the voltagecoupling between the electrodes 62 and 70 is equal to or greater thanthe coupling that exists when the swing plate 64 is pressed up againstthe dielectric 22 of FIG. 4.

Although various specific embodiments of the invention are shown in thedrawings and described in the foregoing specification, it will beunderstood that invention is not limited to the specific embodimentsdescribed, but is capable of modification and rearrangement andsubstitution of parts and elements without departing from the spirit ofthe invention.

What is claimed is:

l. A variable capacitance device comprising:

a first conductor with at least one planar surface;

a second conductor with at least one planar surface;

a third conductor with at least one planar surface and having at leastone edge;

a fourth conductor with at least one planar surface and having at leastone edge; means for mounting the edge of the third conductorsubstantially in the plane of the surface of the first conductor;

means for mounting the edge of the fourth conductor substantially in theplane of the surface of the second conductor;

a push button;

means responsive to at least some movement of the push button forpivoting the third conductor substantially along the edge thereof foraltering the average distance between the surface of the first conductorand the surface 5 of the third conductor, whereby the capacitivecoupling between the first and third conductors is altered; and meansresponsive to further movement of the push button for pivoting thefourth conductor along the edge thereof for altering the averagedistance between the surface of the second conductor and the surface ofthe fourth conductor, whereby the capacitive coupling between the secondand fourth conductors is altered after the alteration of the capacitivecoupling between the first and third conductors. 2. A device'accordingto claim 1, wherein the two pivoting means comprise:

first means for normally biasing the third conductor to a positionadjacent to the first conductor;

second means for normally biasing the fourth conductor to a positionadjacent to the second conductor;

means responsive to at least some movement of the push button forovercoming the first biasing means and for moving the third conductor toa position remote from the first conductor; and

means responsive to further movement of the push button for overcomingthe second biasing means and for moving the fourth conductor to aposition remote from the second conductor.

3. A variable capacitance device comprising:

a first conductor with at least one planar surface;

a second conductor constructed of magnetically permeable material andhaving at least one planar surface and at least one edge;

means for mounting the edge of the second conductor substantially in theplane of the surface of the first conductor;

a permanent magnet for normally biasing the second conductor to aposition adjacent to the first conductor; and

means for overcoming the bias of the permanent magnet and for pivotingthe second conductor substantially along the edge thereof for increasingthe average distance between the surface of the first conductor and thesurface of the second conductor, whereby the capacitive coupling betweenthe first and second conductors is altered.

4. A variable capacitance device comprising:

a first conductor with at least one planar surface;

a second conductor constructed of a magnetically permeable material andhaving at least one planar surface and at least one edge;

means for mounting the edge of the second conductor substantially in theplane of the surface of the first conductor;

a permanent magnet for normally biasing the second conductor to a firststop position either adjacent to or away from the first conductor;

leverage means for overcoming the attraction of the magnet in responseto the application of force thereto and for moving the second conductorto a second stop position opposite to the first stop position; and

60 means for applying force to the leverage means.

5. A device according to claim 4, wherein the force-applying meanscomprises a spring mounted at one end to the leverage means and havingthe other end positioned for manual energization.

' 6. A device according to claim 5, wherein a manually depressible keyis attached to the other end of the spring.

7. A variable capacitance device comprising:

a first conductor having at least one planar surface;

a second conductor having at least one planar surface;

a third conductor having at least one planar surface arranged to bepositioned substantially parallel with the planar surface of the firstconductor;

a fourth conductor having at least one planar surface arranged to bepositioned substantially parallel with the planar surface of the secondconductor;

a dielectric surface on at least one of the first and third conductors;

a dielectric surface on at least one of the second and fourthconductors;

a manually movable push button;

first means responsive to at least some movement of the push button foraltering the distance between the first and third conductors in adirection substantially perpendicular to the planar surface of at leastone of the first and third conductors, whereby the capacitive couplingbetween the first conductor and the third conductor is altered; and

second means responsive to further movement of the push button foraltering the distance between the second and fourth conductors in adirection substantially perpendicular to the planar surface of at leastone of the second and fourth conductors, whereby the capacitive couplingbetween the second conductor and the fourth conductor is altered afterthe capacitive coupling between the first and third conductors isaltered,

8. A device according to claim 7, further comprising:

first means for biasing the first and third conductors in closeproximity to each other;

second means for biasing the second and fourth conductors in closeproximity to each other;

wherein the first altering means comprises means responsive to somemovement of the push button for overcoming the first biasing means; and

wherein the second altering means comprises means responsive to furthermovement of the push button for overcoming the second biasing meansafter the first biasing means has been overcome.

9. A variable capacitance device comprising:

a first conductor having at least one planar surface;

a second conductor having at least one planar surface arranged to bepositioned substantially parallel with the planar surface of the firstconductor;

at least one of the first and second conductors being constructed of aferromagnetic material;

a sheet of solid dielectric material adhered to the surface of at leastone of the first and second conductors;

means for biasing the first and second conductors in close proximity toeach other;

means responsive to a mechanical input for overcoming the biasing meansand for altering the distance between the first and second conductors ina direction between substantially perpendicular to the planar surface ofat least one of the first and second conductors, whereby the capacitivecoupling between the first conductor and the second conductor isaltered.

10. A device according to claim 9, wherein the biasing means comprises amagnet.

11. A device according to claim 10, wherein the magnet is a permanentmagnet.

12. A device according to claim 11, wherein the permanent magnet ispositioned adjacent the other of the first and second conductors and onthe side opposite the ferromagnetic conductor, wherein the ferromagneticconductor is attracted toward the other conductor.

13. A device according to claim 9, wherein only one of the conductors isconstructed of ferromagnetic material and the other of the conductors isdisposed so that the biasing means comprises magnetic force normallyattracting the ferromagnetic conductor toward the permanent magneticconductor.

14. A variable capacitance device comprising:

a conductor with at least one planar surface;

a second conductor with at least one planar surface and having at leastone edge;

said second conductor being shaped to form a bend at the edge thereofwith an elongated projection from said bend, said projection having anend remote from said bend;

a comer substantially in the plane of the surface of the firstconductor; the second conductor positioned with the bend thereofpivotally mounted substantially in the corner; and

means for applying a force to the end of the elongated projection of thesecond conductor for pivoting the second conductor substantially alongthe edge thereof at its bend for altering the average distance betweenthe surface of the first conductor and the surface of the secondconductor, whereby the capacitive coupling between the first and secondconductors is altered.

15. A device according to claim 14, wherein the pivoting meanscomprises:

means for normally biasing the second conductor to a position adjacentto the first conductor; and

means for overcoming the biasing means and for moving the secondconductor to a position remote from the first conductor.

16. A device according to claim 15 wherein the overcoming meanscomprises:

a push button; and

means interconnecting the push button with the end of the projection onthe second conductor.

17. A device according to claim 16 wherein the coupling comprises aspring.

18. An improved capacitive switch of the type including a pair of spacedconductive plates, one of which is movable between first and secondpositions to vary the spacing between the plates and thus thecapacitance, wherein the improvement comprises:

a magnet for normally biasing the movable plate to the first position,the movable plate being made of ferromagnetic material; and

a mechanical linkage for shifting the movable plate to the secondposition against the biasing action of the magnet, for changing thestate of the switch.

1. A variable capacitance device comprising: a first conductor with atleast one planar surface; a second conductor with at least one planarsurface; a third conductor with at least one planar surface and havingat least one edge; a fourth conductor with at least one planar surfaceand having at least one edge; means for mounting the edge of the thirdconductor substantially in the plane of the surface of the firstconductor; means for mounting the edge of the fourth conductorsubstantially in the plane of the surface of the second conductor; apush button; means responsive to at least some movement of the pushbutton for pivoting the third conductor substantially along the edgethereof for altering the average distance between the surface of thefirst conductor and the surface of the third conductor, whereby thecapacitive coupling between the first and third conductors is altered;and means responsive to further movement of the push button for pivotingthe fourth conductor along the edge thereof for altering the averagedistance between the surface of the second conductor and the surface ofthe fourth conductor, whereby the capacitive coupling between the secondand fourth conductors is altered after the alteration of the capacitivecoupling between the first and third conductors.
 2. A device accordingto claim 1, wherein the two pivoting means comprise: first means fornormally biasing the third conductor to a position adjacent to the firstconductor; second means for normally biasing the fourth conductor to aposition adjacent to the second conductor; means responsive to at leastsome movement of the push button for overcoming the first biasing meansand for moving the third conductor to a position remote from the firstconductor; and means responsive to further movement of the push buttonfor overcoming the second biasing means and for moving the fourthconductor to a position remote from the second conductor.
 3. A variablecapacitance device comprising: a first conductor with at least oneplanar surface; a second conductor constructed of magnetically permeablematerial and having at least one planar surface and at least one edge;means for mounting the edge of the second conductor substantially in theplane of the surface of the first conductor; a permanent magnet fornormally biasing the second conductor to a position adjacent to thefirst conductor; and means for overcoming the bias of the permanentmagnet and for pivoting the second conductor substantially along theedge thereof for increasing the average distance between the surface ofthe first conductor and the surface of the second conductor, whereby thecapacitive coupling between the first and second conductors is altered.4. A variable capacitance device comprising: a first conductor with atleast one planar surface; a second conductor constructed of amagnetically permeable material and having at least one planar surfaceand at least one edge; means for mounting the edge of the secondconductor substantially in the plane of the surface of the firstconductor; a permanent magnet for normally biasing the second conductorto a first stop position either adjacent to or away from the firstconductor; leverage means for overcoming the attraction of the magnet inresponse to the application of force thereto and for moving the secondconductor to a second stop position opposite to the first stop position;and means for applying force to the leverage means.
 5. A deviceaccording to claim 4, wherein the force-applying means comprises aspring mounted at one end to the leverage means and having the other endpositioned for manual energization.
 6. A device according to claim 5,wherein a manually depressible key is attached to the other end of thespring.
 7. A variable capacitance device comprising: a first conductorhaving at least one planar surface; a second conductor having at leastone planar surface; a third conductor having at least one planar surfacearranged to be positioned substantially parallel with the planar surfaceof the first conductor; a fourth conductor having at least one planarsurface arranged to be positioned substantially parallel with the planarsurface of the second conductor; a dielectric surface on at least one ofthe first and third conductors; a dielectric surface on at least one ofthe second and fourth conductors; a manually movable push button; firstmeans responsive to at least some movement of the push button foraltering the distance between the first and third conductors in adirection substantially perpendicular to the planar surface of at leastone of the first and third conductors, whereby the capacitive couplingbetween the first conductor and the third conductor is altered; andsecond means responsive to further movement of the push button foraltering the distance between the second and fourth conductors in adirection substantially perpendicular to the planar surface of at leastone of the second and fourth conductors, whereby the capacitive couplingbetween the second conductor and the fourth conductor is altered afterthe capacitive coupling between the first and third conductors isaltered.
 8. A device according to claim 7, further comprising: firstmeans for biasing the first and third conductors in close proximity toeach other; second means for biasing the second and fourth conductors inclose proximity to each other; wherein the first altering meanscomprises means responsive to some movement of the push button forovercoming the first biasing means; and wherein the second alteringmeans comprises means responsive to further movement of the push buttonfor overcoming the second biasing means after the first biasing meanshas been overcome.
 9. A variable capacitance device comprising: a firstconductor having at least one planar surface; a second conductor havingat least one planar surface arranged to be positioned substantiallyparallel with the planar surface of the first conductor; at least one ofthe first and second conductors being constructed of a ferromagneticmaterial; a sheet of solid dielectric material adhered to the surface ofat least one of the first and second conductors; means for biasing thefirst and second conductors in close proximity to each other; meansresponsive to a mechanical input for overcoming the biasing means andfor altering the distance between the first and second conductors in adirection between substantially perpendicular to the planar surface ofat least one of the first and second conductors, whereby the capacitivecoupling between the first conductor and the second conductor isaltered.
 10. A device according to claim 9, wherein the biasing meanscomprises a magnet.
 11. A device according to claim 10, wherein themagnet is a permanent magnet.
 12. A device according to claim 11,wherein the permanent magnet is positioned adjacent the other of thefirst and second conductors and on the side opposite the ferromagneticconductor, wherein the ferromagnetic conductor is attracted toward theother conductor.
 13. A device according to claim 9, wherein only one ofthe conductors is constructed of ferromagnetic material and the other ofthe conductors is disposed so that the biasing means comprises magneticforce normally attracting the ferromagnetic conductor toward thepermanent magnetic conductor.
 14. A variable capacitance devicecomprising: a conductor with at least one planar surface; a secondconductor wiTh at least one planar surface and having at least one edge;said second conductor being shaped to form a bend at the edge thereofwith an elongated projection from said bend, said projection having anend remote from said bend; a corner substantially in the plane of thesurface of the first conductor; the second conductor positioned with thebend thereof pivotally mounted substantially in the corner; and meansfor applying a force to the end of the elongated projection of thesecond conductor for pivoting the second conductor substantially alongthe edge thereof at its bend for altering the average distance betweenthe surface of the first conductor and the surface of the secondconductor, whereby the capacitive coupling between the first and secondconductors is altered.
 15. A device according to claim 14, wherein thepivoting means comprises: means for normally biasing the secondconductor to a position adjacent to the first conductor; and means forovercoming the biasing means and for moving the second conductor to aposition remote from the first conductor.
 16. A device according toclaim 15 wherein the overcoming means comprises: a push button; andmeans interconnecting the push button with the end of the projection onthe second conductor.
 17. A device according to claim 16 wherein thecoupling comprises a spring.
 18. An improved capacitive switch of thetype including a pair of spaced conductive plates, one of which ismovable between first and second positions to vary the spacing betweenthe plates and thus the capacitance, wherein the improvement comprises:a magnet for normally biasing the movable plate to the first position,the movable plate being made of ferromagnetic material; and a mechanicallinkage for shifting the movable plate to the second position againstthe biasing action of the magnet, for changing the state of the switch.